Gas turbine engines are known to operate in extreme environments exposing the engine components, especially those in the turbine section, to high operating temperatures as well as high thermal and mechanical stresses. As a result of such elevated operating conditions, components in the turbine are exposed to large temperature gradients. These temperature gradients can cause significant thermal growth in turbine components. As one skilled in the art will understand the amount of growth of an engine component is a function of the coefficient of thermal expansion for the material and the change in temperature across the component.
In order for the turbine components to endure these conditions, it is necessary to actively cool these components and/or allow for the components to grow or move. While active cooling, such as directing compressor discharge air through or across heated components, is an option, the more air taken from the compressor for cooling, the less efficient the engine, as less air is available for combustion and mechanical work. However, in order to allow for thermal growth among mating components, gaps or spaces are required there between, so as to not create elevated stresses when adjacent parts move and contact each other. Alternatively, allowances can be made for thermal growth by reducing the stiffness of components by increasing their flexibility or ability to move with temperature changes. However, often times this increase in flexibility requires smaller, yet a greater quantity of components, in order to be equivalent to a larger, single piece design.
An example of a gas turbine engine component subject to these conditions is found in the turbine section. More particularly, one feature, common in larger gas turbine engines, is a static structure known as a turbine support ring. As one skilled in the art will understand, this ring is typically positioned radially outward of a stage of stationary airfoils (vanes) and serves to hold the vanes in place. This ring can also hold a set of shroud blocks or outer air seals that are positioned radially outward of a stage of rotating airfoils (blades). Cooling air for the vanes or shroud blocks is typically directed through the support ring. This support ring can often be exposed to a temperature gradient of up to 250 degrees F.
Referring to FIG. 1, a portion of a prior art turbine support ring is shown. This ring was split into numerous sections 100 so as to allow for the thermal growth. In fact, depending on the size of the ring in question, there can be up to 48 sections. That means there are up to 48 gaps through which the air can leak if not properly sealed. Seals were placed in between sections 100 in an attempt to control the air leakage. However, these gaps still leaked. For example, for the first stage of turbine vanes in a land-based gas turbine engine, these gaps leaked approximately 2.2% of the total cooling air supplied to this stage of the turbine. The leakage of cooling air results in reduced cooling air effectiveness, thereby requiring more air to cool the components. As a result, that is less air to be directed through the combustor and turbine, thereby lowering efficiency of the turbine. In addition to the leakage issues, assembling a ring with numerous segments (up to 48) and corresponding seals is a tedious and time-consuming process.